Apparatus for preparing salt cavities by solution



Oct. 11, 1955 c. H. BROOKS APPARATUS FOR PREPARING SALT CAVITIES BY SOLUTION Filed Feb. 25, 1953 2 Sheets-Sheet l INVENTOR. CHARLES H. BROOKS 0X30. spam;

ATTORNEY Oct. 11, 1955 c. H. BROOKS 2,720,390

APPARATUS FOR PREPARING SALT CAVITIES BY SOLUTION Filed Feb. 25, 1-953 2 Shets-Sheet 2 Fig.4

u g i i I i INVENTOR.

CHARLES H. BROOKS ATTORN EY United States Patent APPARATUS FOR PREPARING SALT CAVITIES BY SOLUTION Charles H. Brooks, Swarthmore, Pa., assignor to Sun Oil fompany, Philadelphia, Pa a corporation of New ersey Application February 25, 1953, Serial No. 338,860 2 Claims. (Cl. 262-3) This invention relates to the preparation of under ground salt cavities and more particularly relates to apparatus for the eflicient preparation of underground salt cavities useful for the storage of hydrocarbons.

The preparation of underground salt cavities for the storage of hydrocarbons has heretofore been accomplished by drilling to a point within an underground salt formation, such as a salt stratum or salt dome. Suitable salt strata are usually from 500 to 4000 feet below the surface of the ground, and may be from about 50 to 1000 feet thick. Salt domes similarly located also may be used. Water is then introduced through tubing to a point near the bottom of the borehole, and brine formed by dissolution of salt in the water is removed through the annulus between the tubing and casing. As the size of the cavity increases the washing action is continued, i. e., water is continuously introduced into the cavity through the tubing at a point near the bottom of the cavity, and brine is continuously removed from the top of the cavity through the borehole, which is the annulus between the tubing and casing. This method, however, is not satisfactory. The dissolution of salt is inefficient, as shown by the fact that the salt concentration of the effluent brine does not even approach saturation. Furthermore, little, if any, control over the shapeof the cavity can be exerted. Fresh water introduced through the tubing is less dense than the brine within the cavity, and hence instead of contacting the walls of the cavity so that salt is dissolved therefrom, there is a strong tendency for the water to rise directly to the top of the cavity where it is removed through the annulus betweenthe tubing and casing. Thus, the salt concentration of the removed brine does not even approachsatur'ation so that a substantially larger quantity of water is required to prepare a eavity of given size than if the effluent brine were substantially saturated. This showsthe poor efiiciency of the process as heretofore performed. Slow circulation does not overcome this difliculty, since the tendency for the less dense water to rise directly to the cavity top' is enhanced by the decreased agitation obtained with slow circulation, and the time required to so prepare a cavity is prohibitive. Furthermore, reversal of the flow of water so that water is introduced at the cavity top and brine is removed from the cavity bottom does not solve theproblem' and in fact presents other difliculties. For example, insoluble matter is normally distributed through salt strata. This material settles to the bottom of the cavity during its preparation. On reversal of the flow of water so that brine is removed from the cavity bottom, the" settled material will also be removed and plug the conduits, pumps,-and the like, through whichit flows togetherwith eflluent' brine.

An object of the present invention is to provide new apparatus for the preparation of sub-surface salt cavities. Another'object is toprovide 1 an apparatus for the e'flicient preparation of sub-surfacesalt cavities whereinthe water required todissolve salt 'is substantially"less-thanrequired by processes heretofore used. A further object is to provide an apparatus whereby a sub-surface salt cavity of a desired shape can be prepared. Other objects appear hereinafter.

The drawings illustrate the apparatus of the present invention. Figure l is a side elevation showing the apparatus in position for insertion into the borehole leading to a sub-surface salt formation, and by phantom lines shows the apparatus positioned for preparing the salt cavity in accordance with the present invention. Figure 2 is a cross-section view showing a special portion of the apparatus. Figure 3 is a cross-section view showing a special embodiment of the apparatus. Figure 4 shows the apparatus in use in the preparation of a salt cavity. The drawings are fully explained hereinafter.

Patent application Serial No. 323,905, filed December 3, 1952, now abandoned, describes and claims an apparatus for applying coating material in the liquid phase to the surface of sub-surface salt cavities. The apparatus of Serial No. 323,905 comprises a semi-rigid tubing with means at one end, such as a coupling, so that the tubing can be connected with a rigid conduit, such as a pipe, through which liquid coating material is introduced. By semi-rigid tubing is meant a tubing so constructed that a force tending to bend the tubing" will cause it to bend in a substantially even arc. The other end of the tubing terminates with a spray nozzle, the design of which is dependent upon the fluid material used and the size of the space being coated. A flexible cable, such as a wire, is attached to the nozzle end of the tubing and extends along the tubing at least as far as the coupling, the cable being held in place adjacent and substantially parallel to the axis of the tubing by a series of Wire guides which are mounted on the tubing along a line substantially parallel to the axis of the tubing. In operation, the semi-rig'id tubing is connected to a rigid conduit, preferably a pipe, and is inserted into the salt cavity or other confined space to be treated. Tension on the cable is increased so that the tubing bends to form an arc with the cable guides positioned along the interior of the arc. Fluid is then pressured through the conduit and tubing and is sprayed through the nozzle onto the inner surface of the container. By rotating the conduit and gradually increasing or releasing the tension on the cable, the entire inner surface of the confined locality is contacted with the coating material. The conduit may also be raised and lowered to move the apparatus up and down and thus assist in the coating operation.

The apparatus of the present invention comprises the combination of a portion of the apparatus described in Serial No. 323,905with a mixing eductor. The nozzle used for spraying coating material, which is attached to one end of the flexible tubing of Serial No. 323905, is replaced with a mixing eductor, as hereinafter described, to form the apparatus of the present invention. This combination results in substantial and unobvious benefits when used, as hereinafter described, for the preparation of sub-surface salt cavities.

A mixing eductor is a device wherein a fluid, designated as jet fluid, such as water, is discharged at relatively high velocities through a converging tube, i. e., a tube having a venturi throat Another fluid, designated as suction fluid, in which the mixing. eductor is immersed, is entrained by the jet fluid andcarried through the tube, wherein the two fluids are intimately mixed. This action is more fully explained hereinafter Attention is now directed to Figure l, which is a side elevation showing the apparatus in position for insertion into the borehole leading to a sub-surface salt formation. In the drawing, 1 is a semi-rigid tubing attached to a rigid conduit, such as pipe 2, through coupling 4. The other end of tubing 1 is attached to block 5 which supports a mixing eductor shown broadly as 6. Preferably block 5 is designed so that the eductor can be changed as desired. Cable guides 8 are mounted on tubing 1 along a line parallel to the axis of the tubing. Flexible cable 9 passes through cable guides 8 and is in slidable connection therewith; the end of cable 9 is attached to block 5 at 10. A second flexible cable 11 is preferably employed. Cable 11 is attached to mixing eductor 6 through connector 3 and extends in slidable connection through guide 12 mounted at a point above flexible tubing 1, such as on coupling 4. Cable 9 may also pass through guide 12, as shown. Mixing eductor 6 comprises nozzle 14 through which liquid is discharged into converging tube 15, which is attached to the apparatus through fins 16 and block 17. The apparatus, as shown by phantom lines, has the same parts designated by the same numbers. It will be noted that to obtain this position the tension on cable 9 has been increased so that this cable is positioned against the tops of cable guides 8, and that cable guides 8 are positioned along a line parallel to the axis of the tubing along the interior of the are formed by the tubing. It will be further noted that cable 11 is used to support the apparatus in this position and to assist in obtaining this position, if necessary, by increasing the tension on cable 11 simultaneously with increasing the tension on cable 9.

Figure 2 is a cross-section of mixing eductor 6 showing nozzle 14 extending through block 17. Fluid 18, the jet fluid which is 'water, is discharged through nozzle 14 into converging tube 15, nozzle 14 and tube 15 being connected through block 17 and fins 16. In operation eductor 6 is immersed in the brine filling the cavity, which is the suction fluid, so that space 19 is filled therewith. A portion of the brine in space 19 is entrained in water 18 and is carried through converging tube 15, wherein they are intimately admixed. This entrainment causes a suction at space 19 which draws in additional brine surrounding the ejector, which in turn is entrained and carried through tube 15. In Figure 2, cable 11 is shown attached to connector 3A, and connector 3A is attached to ring 7 which is slidably mounted on eductor 6 between collars 13. This special embodiment for connecting cable 11 to eductor 6 is more fully described hereinafter.

To illustrate a method of employing the apparatus, the semi-rigid tubing terminating with a mixing eductor is inserted into a borehole and positioned within a subsurface salt formation. Water is then introduced through the pipe and mixing eductor to dissolve contacting salt, brine being removed through the annulus between the pipe and easing. As the cavity enlarges, tension on the flexible cable is increased and the flexible tubing thus bent so that the mixing eductor reaches a horizontal position. This directs the flow of Water directly against a side of the cavity. By rotating, raising or lowering the pipe, the eductor may be positioned in any direction at any level. By thus directing inflowing water against any desired portion of the cavity surface, the salt of that portion is more rapidly dissolved than from the remaining surface, and in this manner the shape of the cavity is controlled. Through the action of eductor in admixing the relatively dilute brine within the cavity, in which the eductor is immersed with incoming water, vigorous agitation within the cavity is achieved so that substantially saturated brine is removed through the annulus. In this manner, through the mixing action of the eductor, passage of fresh water or water having only a small concentration of salt directly to the top of the cavity is prevented, and the quantity of water required to prepare a cavity of given size is substantially reduced. Through the apparatus of the invention, comprising the combination of a flexible tube and a mixing eductor, as herein described, a cavity can be rapidly and efficiently prepared to substantially any size and shape desired.

The semi-rigid tubing may be constructed of any suitable material, such as rubber or plastic, or it may be a semi-rigid spirally wound tube from band material such as steel, brass, and the like. The tubing should be at least as long as /2 of the circumference of the minimum diameter circle to which the tubing can be bent by the means herein described without substantial deformation. Practical considerations will usually dictate a length of from 3 to 20 feet. The cable guides may be mounted on the tube by any convenient means, such as by soldering or welding when the tube is metal, or by mounting the guides on thin metal bands extending around the tube when rubber or plastic is employed. The cable guides must be spaced apart so that they do not touch on bending the tube through an arc of about and at least six cable guides, not including the connection of the cable to the nozzle block, preferably should be used, but with some semirigid tubings a smaller number, usually not less than four, may be employed.

The mixing eductor may be prepared of any suitable material, such as cast iron or bronze. In some applications, however, the weight of such materials of construction makes the operation difficult and hence the use of a plastic material, such as phenol-formaldehyde or methyl methacrylate resins, or other plastic material resistant to the action of brine, is preferred in some instances. The dimensions of the eductor, including the nozzle and converging tube, are dependent upon the volume of water to be introduced per unit time and the pressure differential existing between the water in the nozzle and the pressure within the cavity. It is preferred to employ an eductor and pressure differential so that from 1 to 3 or more parts of brine immersing the eductor is entrained and carried through the converging tube per part of jet water introduced.

Attention isnow directed to Figure 3, which shows in cross-section a special embodiment of the apparatus of the invention, in which a plurality of cables circumferentially spaced around the tubing extend from the block carrying the eductor parallel to the tubing and each other. The semi-rigid tubing is represented in cross-section by 1a. Four cable guides 8a are equally spaced around the circumference of tubing 1a, with cables 9a passing therethrough. The other features of the apparatus are as shown in Figures 1 and 2. This embodiment has several advantages. In the event the rigid liquid supply conduit cannot be rotated, the flexible tubing may be used to direct the eductor toward a portion of the surface of a salt cavity by increasing or decreasing the tension on one cable while the remaining cables are slack. The remaining portions of the confined locality are contacted by inflowing water by operating the other cables in like manner. By using an appropriate number of cables the eductor can be directed toward substantially any portion of the salt cavity and a cavity of a desired size and shape rapidly and economically prepared without rotating the apparatus by rotating the rigid conduit. In using a plurality of cables as shown in this embodiment, the cable attached to the eductor (not shown in Figure 3) is advantageously attached therewith through a connection which is slidable around the eductor. This embodiment, having the cable attached to the eductor through a connection that is slidable around the eductor is illustrated in Figure 2, to which attention is again directed. As shown in Figure 2, cable 11 is attached to connector 3A. Connector 3A is connected to ring 7. Ring 7 is rotatably mounted on eductor 6 between collars 13. Ring 7, bear ing connector 3A, is thus rotatable about the eductor and is prevented from longitudinal movement relatively to the eductor by collars 13. In this manner, the cable connection is maintained at the top of the eductor when the direction thereof is changed as described above. If desired, a plurality of cables can be attached to and circumferentially spaced around the eductor, in which eventthe cable attached to the top of the eductor is employed t ma n ain the @dHQtQI in the desired horizontal position,

the remaining cables also attached to the eductor being slack. A further advantage of this embodiment is where the semi-rigid tubing, after bending by increasing the tension on a cable, does not return to its original position for easy removal from the confined locality. With a cable positioned on the tubing opposite the cable initially used to bend the tubing, the tubing can easily be returned to its original position by increasing the tension of this cable after releasing the tension on the cable initially used. Although four cables are shown in Figure 3, a different number may be employed if necessary or desirable.

Attention is now directed to Figure 4 which illustrates the process of the present invention. An underground salt formation, which may be a salt stratum or a salt dome, is illustrated by 30. Salt formation 30 is in communication with the ground surface 31 by borehole 32 bounded by casing 34. Conduit 35 is a pipe for supplying Water from the ground surface into the cavity through the apparatus of the invention shown broadly by 36, which includes flexible tube 1 and eductor 6. As shown, the process has advanced to a stage Where a substantial cavity has been formed and enlargement of the cavity, as shown by 38, is in progress. The apparatus is shown with mixing eductor 6 in a horizontal direction obtained by increasing the tension on cable 9 and securely held in position by cable 11. By operating as herein described, the cavity may be made to a desired shape. For example, the cavity can be made in the form of a sphere, cylinder or pear shape.

The process of the present invention can be illustrated with reference to the preparation of a salt cavity of about 50,000 barrels capacity to be used for the storage of hydrocarbons. A borehole was drilled to a point within a salt stratum at a depth of about 2,600 feet. In accordance with usual practice, water was introduced into the cavity to dissolve salt, and brine was removed therefrom, the water being introduced through a pipe at the bottom of the cavity, and brine being removed through the annulus between the tubing and easing at the top of the cavity. During preparation of the cavity, water was injected at a rate of 7,000 barrels per day, and the same quantity of brine was removed from the cavity. The efliuent brine had a density at of from 1.07 to 1.12, i. e., the concentration of salt was from about 0.89 to 1.56 pounds per gallon of water.

On employing the apparatus of the present invention, as above described, with other operating variables the same, the efiluent brine has a density of from about 1.16 to about 1.19 or even higher, i. e., the concentration of salt is from about 1.99 to about 2.5 pounds per gallon of water. Thus, by injecting the same quantity of Water the cavity is produced in about one half the time heretofore required. Also, as above described, the shape of the cavity can be controlled, and the plugging of conduits, pumps, and the like by insoluble matter is not observed, since such matter settles to the bottom of the cavity and hence does not appear in the eflluent brine.

The invention claimed is:

1. An apparatus for continuously supplying water to a sub-surface salt formation to prepare a cavity therein by dissolution of salt in the water which comprises a semirigid tubing, means adjacent one end of said tubing adapted to connect with a fluid supply conduit, a mixing eductor terminating the other end of said tubing, a flexible cable attached to the eductor end of said. tubing and extending adjacent said tubing, a series of cable guides mounted on and extending along a line substantially parallel to the axis of said tubing relatively to which the cable is slidable along the tubing to thereby maintain the cable adjacent the tubing, and a second flexible cable attached to said eductor and attached in slidable connection with a cable guide positioned beyond the end of the flexible tubing having means adapted to connect with a fluid supply conduit.

2. An apparatus for continuously supplying water to a sub-surface salt formation to prepare a cavity therein by dissolution of salt in the water which comprises a semirigid tubing, means adjacent one end of said tubing adapted to connect with a fluid supply conduit, a mixing eductor terminating the other end of said tubing, a plurality of flexible cables attached to the nozzle end of said tubing and extending adjacent said tubing, said cables being circumferentially spaced adjacent said tubing, a plurality of series of cable guides circumferentially mounted on and extending along lines substantially parallel to the axis of the tubing and relatively to which the cables are respectively slidable along the tubing to thereby maintain the cables adjacent the tubing, and a second flexible cable attached to said eductor through a connection which is slidable around the eductor, said second flexible cable also being attached in slidable connection with a cable guide positioned beyond the end of the flexible tubing having means adapted to connect with a fluid supply conduit.

References Cited in the file of this patent UNITED STATES PATENTS 671,429 Bacon Apr. 9, 1901 2,251,916 Cross Aug. 12, 1941 2,577,797 Mayer Dec. 11, 1951 

1. AN APPARATUS FOR CONTINUOUSLY SUPPLYING WATER TO A SUB-SURFACE SALT FORMATION TO PREPARE A CAVITY THEREIN BY DISSOLUTION OF SALT IN THE WATER WHICH COMPRISES A SEMIRIGID TUBING, MEANS ADJACENT ONE END OF SAID TUBING ADAPTED TO CONNECT WITH A FLUID SUPPLY CONDUIT, A MIXING EDUCTOR TERMINATING THE OTHER END OF SAID TUBING, A FLEXIBLE CABLE ATTACHED TO THE EDUCTOR END OF SAID TUBING AND EXTENDING ADJACENT SAID TUBING, A SERIES OF CABLE GUIDES MOUNTED ON AND EXTENDING ALONG A LINE SUBSTANTIALLY PARALLEL TO THE AXIS OF SAID TUBING RELATIVELY TO WHICH THE CABLE IS SLIDABLE ALONG THE TUBING TO THEREBY MAINTAIN THE CABLE 